Fuel cell stack assembly and method of operating the same

ABSTRACT

A fuel cell stack assembly and method of operating the same are provided. The assembly includes a fuel cell stack column and side baffles disposed on opposing sides of the column. The side baffles and the fuel cell stack may have substantially the same coefficient of thermal expansion at room temperature. The side baffles may have a laminate structure in which one or more channels are formed.

FIELD

Aspects of the present disclosure relate generally to a fuel cell stackassembly and a method of operating the same.

BACKGROUND

U.S. application Ser. No. 11/656,563, filed on Jan. 23, 2007 andpublished as US published application 2007/0196704 A1 and incorporatedherein by reference in its entirety, describes a fuel cell system inwhich the solid oxide fuel cell (SOFC) stacks are located on a base, asshown in FIG. 1. Wedge shaped ceramic side baffles 220 (e.g., having anon-uniform thickness and a roughly triangular cross sectional shape inthe horizontal direction) are located between adjacent fuel cell stacks14 (or columns of fuel cell stacks). The baffles 220 serve to direct thecathode feed into the cathode flow paths and to fill the space betweenadjacent stacks so that the cathode feed passes through each of thestacks 14, rather than bypassing around the longitudinal sides of thestacks 14. The baffles 220 are held in place by tie rods 222 that passthrough closely fitting bores 224 centrally located in each of thebaffles 220. Preferably, the baffles 220 are electrically non-conductiveand made as one unitary piece from a suitable ceramic material. FIG. 1also shows fuel distribution manifolds between the stacks in the stackcolumn and fuel inlet and exhaust conduits connected to the manifolds.

In this prior art system, the SOFC stacks maintain a compressive load.The compressive load is maintained by upper pressure plate 230, tie rods222, lower pressure plate 90 and a compression spring assembly locatedbelow the lower pressure plate 90. The compression spring assemblyapplies a load directly to the lower pressure plate 90 and to the upperpressure plate 230 via the tie rods 222. The bores or feed-throughs 224through the baffles 220 act as heat sinks and thereby decrease thesystem efficiency.

In an alternative embodiment, the load is transmitted through the base239 as this is the only zero datum of the system. Penetrations orfeed-throughs through the base 239 are used in order to pull therequired load from the base 239.

SUMMARY

According to various embodiments, provided is a fuel cell stack assemblycomprising: a fuel cell stack column; and side baffles disposed onopposing sides of the column. The side baffles have a first coefficientof thermal expansion (CTE) at room temperature, the column has a secondCTE at room temperature, and the first CTE is within +/−20%, such aswithin +/−10% of the second CTE.

According to various embodiments, provided is a fuel cell stack assemblycomprising: a fuel cell stack column; and side baffles disposed onopposing sides of the column. The side baffles may comprise first andsecond baffle plates that are laminated to one another and comprisedifferent ceramic materials.

According to various embodiments, provided is a fuel cell stack assemblycomprising: a fuel cell stack column; and side baffles disposed onopposing sides of the column. The side baffles may comprise first,second, and third baffle plates that are laminated to one another, withthe second baffle plate being disposed between the first and thirdbaffle plates. At least one of the second baffle plates compriseschannels that extend in a direction perpendicular to a stackingdirection of fuel cells of the column.

According to various embodiments a fuel cell stack assembly comprising:a fuel cell stack column; an upper block disposed on a first end of thecolumn; a lower block having a laminate structure and disposed on anopposing second end of the column; and side baffles disposed on opposingsides of the column and connected to the compression assembly and thelower block. The lower block may comprise: an inlet manifold extendingthere through and connected to an inlet of the column; and an outletmanifold extending there through and connected to an outlet of thecolumn.

According to various embodiments, provided is a method of operating afuel cell stack assembly comprising a fuel cell stack column, sidebaffles disposed on opposing sides of the column, and at least onechannel extending through one of the side baffles, the method comprisingat least one of: flowing air through the at least one channel to coolthe column; flowing fuel through the at least one channel to the column;electrically bypassing at least one fuel cell of the column using abypass electrodes disposed in a plurality of the channels which includethe at least one channel; and detecting a characteristic of the columnusing a sensor or electrical lead disposed in at least one channel.

According to various embodiments, provided is a fuel cell stack assemblycomprising: a fuel cell stack column; a compression assembly configuredto apply pressure to the column; and an upper plate assembly upon whichthe compression assembly is disposed. The upper plate assemblycomprises: a rod plate upon which the compression assembly is disposed;a termination plate disposed between the rod plate and an end plate ofthe column; an interface seal disposed between the termination plate andthe end plate; and a shim disposed between the termination plate and therod plate.

According to various embodiments, provided is a fuel cell stack assemblycomprising: a fuel cell stack column; a compression assembly configuredto apply pressure to the column; and an upper plate assembly upon whichthe compression assembly is disposed. The upper plate assemblycomprises: a rod plate upon which the compression assembly is disposed;a termination plate disposed between the rod plate and an end plate ofthe column; and an interface seal disposed between the termination plateand the end plate.

According to various embodiments, provided is a fuel cell stack assemblycomprising: a fuel cell stack column; a compression assembly configuredto apply pressure to the column; and an upper plate assembly upon whichthe compression assembly is disposed. The upper plate assemblycomprising: a rod plate upon which the compression assembly is disposed;a termination plate disposed between the rod plate and an end plate ofthe column, the termination plate comprising 94-96 wt % Cr and 4-6 wt %Fe; and an interface seal disposed between the termination plate and theend plate.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate exemplary embodiments of theinvention, and together with the description serve to explain theprinciples of the invention.

FIG. 1 illustrates a three dimensional view of a conventional fuel cellassembly.

FIG. 2 illustrates a three dimensional view of a fuel cell stackassembly according to an exemplary embodiment of the present disclosure.

FIG. 3 illustrates a three dimensional view of a fuel cell stackassembly according to an exemplary embodiment of the present disclosure.

FIG. 4 illustrates an exploded view of a compression assembly accordingto an exemplary embodiment of the present disclosure.

FIG. 5 illustrates a cross-sectional view of a compression assemblyaccording to an exemplary embodiment of the present disclosure.

FIGS. 6A and 6B are schematic front views of a fuel cell stack assemblyat 20° C. and 700° C., respectively.

FIG. 7A is a schematic side view of baffle plates of a modified versionof the fuel cell stack assembly of FIG. 2, according to an exemplaryembodiment of the present disclosure.

FIG. 7B is a schematic side view of baffle plates of a modified versionof the fuel cell stack assembly of FIG. 2, according to an exemplaryembodiment of the present disclosure.

FIG. 8 is a schematic front view of a fuel cell stack assembly accordingto an exemplary embodiment of the present disclosure.

FIG. 9 is a schematic front view of a modified version of the fuel cellstack assembly of FIG. 8.

FIG. 10 is a schematic front view of another modified version of thefuel cell stack assembly of FIG. 8.

FIG. 11 is a cross-sectional schematic front view of another modifiedversion of the fuel cell stack assembly of FIG. 8, taken through a planein which bypass electrodes and sensors extend.

FIG. 12A illustrates a perspective view of a portion of a fuel cellstack assembly, according to various embodiments of the presentdisclosure.

FIG. 12B illustrates a side view of an upper plate assembly of the fuelcell stack assembly of FIG. 12A.

FIG. 13 illustrates a perspective view of a rod plate of the upper plateassembly of FIG. 12B.

FIG. 14A is a finite element model (FEM) showing load distribution on atermination plate during maximum loading.

FIG. 14B is a FEM showing vertical deflections of a termination plateduring maximum loading.

FIG. 14C is a FEM showing stress applied to a rod plate during maximumloading.

FIG. 15 is a sectional view of an upper plate assembly according tovarious embodiments of the present disclosure.

FIG. 16A is a FEM showing load distribution on a termination plateduring maximum loading.

FIG. 16B is a FEM showing vertical deflections of a termination plateduring maximum loading.

FIG. 17A illustrates a modified rod plate according to variousembodiments of the present disclosure.

FIG. 17B is a FEM showing load distribution applied to a rod plateduring maximum loading.

FIG. 17C is a FEM showing bending deflection applied to a rod plateduring maximum loading.

FIG. 17D is a stress vs. time plot comparing maximum stress applied torod plates and corresponding bending deflections of the rod plates andcorresponding termination plates, over time, during initial fuel cellsystem startup.

FIG. 18, which is a stress vs. time plot showing stress and deflectiontest results.

DETAILED DESCRIPTION

The present disclosure is described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theexemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this disclosure is thorough, and willfully convey the scope of the invention to those skilled in the art. Inthe drawings, the size and relative sizes of layers and regions may beexaggerated for clarity. Like reference numerals in the drawings denotelike elements.

It will be understood that when an element or layer is referred to asbeing “on” or “connected to” another element or layer, it can bedirectly on or directly connected to the other element or layer, orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on” or “directly connected to”another element or layer, there are no intervening elements or layerspresent. It will be understood that for the purposes of this disclosure,“at least one of X, Y, and Z” can be construed as X only, Y only, Zonly, or any combination of two or more items X, Y, and Z (e.g., XYZ,XYY, YZ, ZZ).

The bores or feed-throughs 224 of the system of FIG. 1 decrease thesystem efficiency because they create heat sinks. The bores 224 can beeliminated and a compressive load applied to the fuel cell stacks 14 byredesigning the baffles 220. By applying the compressive stress with thebaffles themselves, the tie rods 222 can be eliminated, and thus, thebores 224 can be eliminated. Thus, in one embodiment, the baffles lackbore holes that extend vertically through the baffles and tie rodslocated in the holes.

FIG. 2 illustrates a fuel cell stack assembly 200 according to variousembodiments of the present disclosure. Referring to FIG. 2, the fuelcell stack assembly 200 includes a fuel cell stack column 140, sidebaffles 220 disposed on opposing sides of the column 140, a lower block503, and a compression assembly 600 including an upper block 603. Thecolumn includes three fuel cell stacks 14, fuel manifolds 204 disposedbetween the fuel cell stacks 14, and termination plates 27 disposed onopposing ends of the column 140. The fuel cell stacks 14 include aplurality of fuel cells stacked upon one another and separated byinterconnects. A plurality of the fuel cell stack assemblies 200 may beattached to a base 239, as shown in FIG. 1.

An exemplary fuel manifold 204 is described in the U.S. application Ser.No. 11/656,563 noted above. Any number of fuel manifolds 204 may beprovided between adjacent end plates of adjacent fuel cells of the fuelcell stacks 14, as desired.

The side baffles 220 connect the upper block 603 of the compressionassembly 600 and the lower block 503. The side baffles 220, thecompression assembly 600, and the lower block 503 may be collectivelyreferred to as a “stack housing”. The stack housing is configured toapply a compressive load to the column 140. The configuration of thestack housing eliminates costly feed-throughs and resulting tie rod heatsinks and uses the same part (i.e., side baffle 220) for two purposes:to place the load on the stacks 14 and to direct the cathode feed flowstream (e.g., for a ring shaped arrangement of stacks shown in FIG. 1,the cathode inlet stream, such as air or another oxidizer may beprovided from a manifold outside the ring shaped arrangement through thestacks and the exit as a cathode exhaust stream to a manifold locatedinside the ring shaped arrangement). The side baffles 220 may alsoelectrically isolate the fuel cell stacks 14 from metal components inthe system. The load on the column 140 may be provided by thecompression assembly 600, which is held in place by the side baffles 220and the lower block 503. In other words, the compression assembly 600may bias the stacks 14 of the column 140 towards the lower block 503.

The side baffles 220 are plate-shaped rather than wedge-shaped andinclude baffle plates 202 and ceramic inserts 406 configured to connectthe baffle plates 202. In particular, the baffle plates 202 includegenerally circular cutouts 502 in which the inserts 406 are disposed.The inserts 406 do not completely fill the cutouts 502. The inserts 406are generally bowtie-shaped, but include flat edges 501 rather thanfully rounded edges. Thus, an empty space remains in the respectivecutouts 502 above or below the inserts 406.

The side baffles 220 and baffle plates 202 have two major surfaces andone or more (e.g., four) edge surfaces. One or more of the edge surfacesmay have an area at least 5 times smaller than each of the majorsurfaces. Alternatively, one or more edge surfaces may have an area atleast 4 times or 3 times smaller than at least one of the majorsurfaces. Preferably, the baffle plates 202 have a constant width orthickness, have a substantially rectangular shape when viewed from theside of the major surface, and have a cross sectional shape which issubstantially rectangular. In alternative embodiments, the ceramic sidebaffles 220 are not rectangular, but may have a wedge shapedcross-section. That is, one of the edge surfaces may be wider than theopposing edge surface. However, unlike the prior art baffles, whichcompletely fill the space between adjacent electrode stacks 14, the sidebaffles 220 of this embodiment are configured so that there is spacebetween side baffles 220. In other words, the side baffles 220 of thisembodiment do not completely fill the space between adjacent columns140. In other embodiments, wedge-shaped metal baffles may be insertedbetween adjacent side baffles 220, similar to the configuration shown inFIG. 1.

Generally, the side baffles 220 are made from a high-temperaturetolerant material, such as alumina or other suitable ceramic. In variousembodiments, the side baffles 220 are made from a ceramic matrixcomposite (CMC). The CMC may include, for example, a matrix of aluminumoxide (e.g., alumina), zirconium oxide or silicon carbide. Other matrixmaterials may be selected as well. The fibers may be made from alumina,carbon, silicon carbide, or any other suitable material. The lower block503 and the compression assembly 600 may also be made of the same orsimilar materials. The selection of particular materials for thecompression housing is discussed in detail, below.

Any combination of the matrix and fibers may be used. Additionally, thefibers may be coated with an interfacial layer designed to improve thefatigue properties of the CMC. If desired, the CMC baffles may be madefrom a unitary piece of CMC material rather than from individualinterlocking baffle plates. The CMC material may increase the bafflestrength and creep resistance. If the baffles are made from alumina oran alumina fiber/alumina matrix CMC, then this material is a relativelygood thermal conductor at typical SOFC operating temperatures (e.g.,above 700° C.). If thermal decoupling of neighboring stacks or columnsis desired, then the baffles can be made of a thermally insulatingceramic or CMC material.

Other elements of the compression housing, such as the lower block 503and the compression assembly 600 may also be made of the same or similarmaterials. For example, the lower block 503 may comprise a ceramicmaterial, such as alumina or CMC, which is separately attached (e.g., bythe inserts, dovetails or other implements) to the side baffles 220 andto a system base 239. The use of the ceramic block material minimizescreation of heat sinks and eliminates the problem of linking the ceramicbaffles to a metal base, which introduces thermal expansion interfaceproblems. The selection of particular materials for the components ofthe compression housing is discussed in detail, below.

FIG. 3 illustrates a fuel cell stack assembly 300 according to variousembodiments of the present disclosure. The fuel cell stack assembly 300is similar to the fuel cell stack assembly 200, so only the differencestherebetween will be discussed in detail. Similar elements have the samereference numbers. Fuel rails 214 (e.g. fuel inlet and outlet pipes orconduits) connect to fuel manifolds 204 located between the stacks 14 inthe column.

Referring to FIG. 3, the fuel cell stack assembly 300 includes sidebaffles 220 disposed on opposing sides of the column of fuel cell stacks14. However, each of the side baffles 220 includes only a single baffleplate 202, rather than the multiple baffle plates 202 of the fuel cellstack assembly 200. In addition, the side baffles 220 include ceramicinserts 406 to connect the baffle plates 202 to a compression assembly600 and a lower block 503.

FIG. 4 illustrates an embodiment of a compression assembly 600 that maybe used in conjunction with any of the embodiments described above.Referring to FIG. 4, the compression assembly 600 may be used to apply acompressive load to the column of fuel cell stacks 14. The compressionassembly 600 includes a spring 611. As illustrated, spring 611 is aceramic (e.g., CMC or alumina) leaf spring. A CMC spring is advantageousbecause it may include creep resistant fibers arranged in a direction inthe matrix which resists creep. The ceramic spring can exist in a hightemperature zone and allow for travel from differential thermalexpansion from components applying the load to the stack. However, anyother type of spring or combination of springs may be used. For example,the spring 611 may be a coil spring, a torsion spring, or a volutespring.

The compression assembly 600 may include a rod plate 607 configured toprovide a resilient surface against which the spring 611 can generate acompressive load. Preferably, the rod plate 607 includes retentionbarriers 608 configured to prevent the spring 611 from sliding off therod plate 607. When using a leaf spring, the rod plate 607 may alsoinclude spring support rods 604. In this configuration, the spring 611may be placed on top of the spring support rods 604 in an unstressedcondition (see also FIG. 5).

An upper plate 601 is provided on top of the spring 611, that is, on theopposite side of the spring 611 from the rod plate 607. The upper plate601 may include a spring tensioner 612, in this embodiment a rod, on thebottom of the upper plate 601. The spring tensioner 612 is preferablylocated approximately in the center of the upper plate 601. Thecompression assembly 600 may also be provided with an upper block 603which may include either cutouts 304 (which accept inserts 406 frombaffles as illustrated) or protrusions 303 by which compression assembly600 may be attached to the side baffles 220.

A temporary tightening mechanism may be attached over or to thecompression assembly 600 during the process of connecting the assemblyto the baffles 220. In the embodiment of FIG. 4, this mechanism includesa bracket 602. The bracket 602 may be affixed to the rod plate 607 bybolts as illustrated or by any other suitable mechanism. Movablyattached to the bracket 602 is a temporary tensioner which in thisembodiment comprises a pressure plate 605. As illustrated, the pressureplate 605 is movably attached to the bracket 602 by way of rods 609which slide in elongated slots 606.

The compression load applied by the compression assembly 600 may beadjusted via a pressure adjusting mechanism 610. The pressure adjustingmechanism 610 may be, for example, a screw or bolt which may be raisedor lowered by rotating. In the embodiment illustrated in FIG. 4,lowering the pressure adjusting mechanism 606 causes the pressure plate605 to travel downward. As the pressure plate 605 lowers, it forces theupper block 603 and the upper plate 601 to lower as well. When the upperplate 601 lowers, the spring tensioner 612 is forced against the centerof the spring 611, causing it to bend and thereby apply a load to thespring 611.

In use, the pressure adjusting mechanism 610 is lowered (and the spring611 compressed) until the upper block 603 can be connected (e.g.,hooked) to the side baffles 220. Once the side baffles 220 are connectedvia dovetails, inserts or other implements, the pressure adjustingmechanism 610 is loosened to release the bracket 602. The force of thespring 611, previously “held” by the pressure adjusting mechanism 610,is now transferred to the side baffles 220. Adjustment of thecompressive force on the stack may be attained by fitting shims (notshown) between the compression assembly 600 and the top of the column ofstacks 14 (which sits below the rod plate 607 of the compressionassembly 600). More shims create a tighter compression. The pressureadjusting mechanism 610 provides pretension to allow connection of thecompression assembly 600 to the side baffles 220. The bracket 602,including mechanism 610 and elements 605, 606 and 609 are then removedfrom the fuel cell column before the column is placed into an operatingmode.

FIG. 5 illustrates another embodiment of a compression assembly 600A.This embodiment is similar to the previous embodiment. However, the rodshaped spring tensioner 612 is replaced with a dome shaped springtensioner 612A, where the curved side of the dome is in contact with theupper surface of the spring. Spring support rods 604 contact edgeportions of a lower surface of the spring 611 to induce bending in thespring. Additionally, this embodiment includes spacers 702 which reducesthe distance between the block 603 and the spring 611, thereby reducingthe amount of adjustment required with the temporary tighteningmechanism, such as a bolt or screw (not shown for clarity) to apply aload to the spring 611 through opening 610A.

FIGS. 6A and 6B illustrate are schematic views of a fuel cell stackassembly, which may be any of the above-described fuel cell stackassemblies 200, 300, or another type of fuel cell stack assembly, at 20°C. and 700° C., respectively. Referring to FIGS. 6A and 6B, thecoefficient of thermal expansion (CTE) of the column 140 of fuel cellstacks may be different from the CTE of the side baffles 220. Forexample, the CTE of the column 140 may be about 9.7, at roomtemperature. The CTE of the side baffles 220 may about 7.2 at roomtemperature, if the side baffles 220 are formed of about 99 wt %alumina. Accordingly, as shown in FIGS. 6A and 6B, as the fuel cellstack assembly is heated, the column 140 expands faster than the sidebaffles, resulting in increased deflection of the compression assembly600. As such, the load applied to the column 140 is increased. Althoughcompression assembly 600 is shown, any of the above-describedcompression assemblies may be used.

It is also important to note that the spring constant of the compressionassembly may be highly non-linear. Further, since the compressionassembly is already deflected at 20° C., the additional deflection at700° C. may apply a substantially higher load to the column 140. Basedon modeling, it is calculated that an original load of 350 lbs at roomtemperature can exceed 1000 lbs, when the column 140 heats up to 650° C.(before the interface seals melt). The opposite scenario is also true,in that the load on the column 140 will be reduced significantly, if thecolumn 140 is cooled from a high temperature. The fundamental reason forthis difference is the CTE difference between the column 140 and theside baffles. The increased loading at high temperatures may result indamage to the fuel cell stacks of the column 140 and/or other componentsof the fuel cell stack assembly.

In order to overcome or reduce the above and/or other problems, the sidebaffles 220 of the above embodiments may be configured to have a CTEthat is substantially the same (within about +/−20%, such as +/−10%) asthe CTE of the column 140. According to some embodiments, the CTE of thebaffle plates 202 may be within about +/−5% of the CTE of the column140. The CTE of the side baffles may be altered by altering thecomposition of one or more components of the side baffles 220. Herein,the CTE of an element refers to a CTE of the element at roomtemperature.

For example, when the side baffles each include a single baffle plate202, as shown in the embodiment of FIG. 3, the baffle plates 202 can beformed of a material having a CTE that is similar to the CTE of thecolumn 140. In particular, the CTE of the baffle plates 202 may bewithin about +/−20%, such as +/−10% of the CTE of the column 140. TheCTE of the baffle plates 202 may be controlled by doping or mixingalumina with other ceramic components, or by choosing different materialsets. The following Table 1 includes exemplary ceramic materials thatmay be included in the side baffles and corresponding CTE's. However,the present disclosure is not limited to such materials, as othersuitable materials may be used.

TABLE 1 Material CTE (Room Temperature) Alumina 7.2 Zirconia(Tetragonal) 12 Magnesia 13.5 Alumina-Titania Mixture 9.7Zirconia-Magnesia Mixture 12

As shown in Table 1, an alumina-titania mixture may be prepared to havea CTE of 9.7, which is substantially the same as the CTE of a column offuel cell stacks. As such, a side baffle 220 including analumina-titania mixture expands at substantially the same rate as thecolumn 140, which prevents excessive loading of the column 140 duringheating.

Further, zirconia (tetragonal phase), magnesia, and a zirconia-magnesiamixture exhibit CTE's that are slightly higher than 9.7. As such, sidebaffles 220 including these materials could also prevent excessiveloading of the column 140 during heating. While these materials wouldexpand at a higher rate than the column 140, such a difference can becompensated for by a compression assembly, since the spring constant ofthe compression assembly 600 may be more linear at lower levels ofcompression. Side baffles 220 can include a mixture of alumina andmagnesia, or a mixture of alumina and zirconia, with amount ratios ofthe mixtures configured such that the side baffles 220 and the column140 have substantially the same CTE.

The baffle plates 202 and the ceramic inserts 406 of the side baffles220 may be formed of the same material. However, according to someembodiments, the baffle plates 202 and the ceramic inserts 406 may beformed of different materials that have CTE's that are higher or lowerthan the CTE of the column 140, so long as the total CTE of the sidebaffles 220 is similar to the CTE of the column 140.

FIG. 7A is a schematic view of a fuel cell stack assembly 200A,according to various embodiments of the present disclosure. Referring toFIG. 7A, the fuel cell stack assembly 200A includes a side baffle 220A,an upper block 603, a lower block 503, and a fuel cell stack column (notshown). The side baffle 220A includes first baffle plates 202A andsecond baffle plates 202B, which are alternately disposed. Although notshown, ends of the baffle plates 202A, 202B may be connected to oneanother using ceramic inserts or through interlocking cutouts andprotrusions, as described above.

The baffle plates 202A, 202B are substantially the same size and shape,but have different CTE's. However, the overall CTE of the side baffle220A may be similar to the CTE of a fuel cell stack column. Inparticular, In particular, the CTE of the side baffle 220A may be withinabout +/−20%, such as +/−10% of the CTE of the fuel cell column. Forexample, when the fuel cell stack has a CTE of about 9.7, the sidebaffle 220A may have a CTE ranging from about 8.7 to about 10.7.

According to some embodiments, the first baffle plates 202A may beformed of alumina, which has a CTE of about 7.2, and the second baffleplates 202B may be formed of tetragonal zirconia, which has a CTE ofabout 12. Accordingly, the CTE of the side baffle 220A may be about 9.6,i.e., the average of 7.2 and 12. Thus, the side baffle 220A may have aCTE that is substantially the same as the 9.7 CTE of a typical fuel cellstack column. However, according to some embodiments, the CTE of thefirst side baffle plates 202A may be higher than the CTE of the stack14, and the CTE of the second side baffle plates 202B may be lower thanthe CTE of the stack 14, so long as the total CTE of the side baffle220A is within about +/−20%, such as +/−10% of the CTE of the fuel cellstack column.

While four baffle plates are shown in FIG. 7A, the present disclosure isnot limited to any particular number of baffle plates. In addition,while the first baffle plates 202A and second baffle plates 202B arealternately disposed in FIG. 7A, other arrangements may be utilized, solong as the CTE of the side baffle 220A is similar to that of a fuelcell stack column included in the fuel cell stack assembly 200A.

FIG. 7B is a schematic view of a fuel cell stack assembly 200B,according to various embodiments of the present disclosure. The fuelcell stack assembly 200B is similar to the fuel cell stack assembly200A, so only the difference therebetween will be discussed in detail.

Referring to FIG. 7B, the fuel cell stack assembly 200B includes a sidebaffle 220B, an upper block 603, a lower block 503, and a fuel cellstack column (not shown). The side baffle 220B includes first baffleplates 202C and second baffle plates 202D, which are alternatelydisposed. Although not shown, the baffle plates 202C, 202D may beconnected to one another using ceramic inserts or through interlockingcutouts and protrusions, as described above.

The first and second baffle plates 202C, 202D may include materialshaving different CTE's. However, in contrast to the fuel cell stackassembly 200A, the first and second baffle plates 202C, 202D may havedifferent lengths (i.e., heights in the stack stacking direction). Assuch, that the overall CTE of the side baffle 220B may be set to besubstantially the same as the CTE of the fuel cell stack column, byvarying the lengths of the first and second baffle plates 202C, 202D. Inother words, varying the lengths of the first and second baffle plates202C, 202D allows for the use of a wider variety of ceramic materials,since varying the length of a baffle plates can change the actual linearexpansion of the plate, and thereby compensate for the use of differentmaterials having an average CTE that is not substantially the same asthat of a fuel cell stack column. For example, baffle plates having ahigher CTE may be made relatively shorter, and/or baffle plates having alower CTE may be made relatively longer, to compensate for CTEvariations. However, the lengths of baffle plates that deviate more fromthe CTE of the fuel cell stack column can be adjusted in considerationof the CTE of the other baffle plates, such that the CTE of thecorresponding side baffle is within +/−20%, such as +/−10% of the CTE ofthe fuel cell stack column.

In particular, when considering a side baffle including only two baffleplates 202C, 202D, if the first baffle plate 202C is formed of materialA having a CTE of 7.2, and the second baffle plate 202D is formed ofmaterial B having a CTE of 14, a ratio of the lengths of the first andsecond baffle plates 202C, 202D would be 14/7.2. As such, a length A ofthe first baffle plate 202C and a length B of the second baffle plate202D can be determined using the following Equations 1 and 2:CTE B=CTE A*(Length A/Length B)  Equation 1CTE Stack*Length Stack=CTE A*Length A+CTE B*Length B  Equation 2

Accordingly, the total CTE of a side baffle including two baffle platesmay be adjusted by adjusting the lengths of the baffle plates includedtherein, in view of the materials used to form the baffle plates.Further, the present disclosure is applicable to side baffles thatinclude fewer or additional baffle plates. For example, in the sidebaffle 220B, the total lengths of baffle plates 202C can be used as thelength A, and the total length of the baffle plates 202D can be used aslength B, in Equation 1. Equations 1 and 2 can be expanded to includeadditional components and/or materials, such as a third type of baffleplate. It should also be noted that the CTE of any ceramic inserts usedto connect baffle plates should also be accounted for in determining theCTE of a side baffle.

Conventionally, fuel cell stack assemblies may be disposed in closeproximity to one another, to reduce space requirements. In addition,ceramic components are pressed to a particular design thickness,limiting the functionality thereof to providing structural anddielectric characteristics.

In view of such drawbacks, various embodiments of the above-describedceramic components may be formed of multiple bonded (laminated) layers,which can have internal features/flow paths that are beneficial forimproving dielectric strength, providing flow channels, temperaturecontrol, and instrumentation insertion. With regard to dielectricstrength, ceramic components formed of layers of different materials canbe prepared. For example, layers of ceramic components that are disposedrelatively close to a fuel cell stack column may include materialshaving a higher dielectric strength, such as different ceramiccompositions, different purities of alumina, and CMCs, than layersdisposed further from the stack.

Ceramic components may also include layers of different thermalconductivity to manage the thermal profile of the fuel cell stackcolumn. Further, layers can be configured provide space forinstrumentation, such as probes, stress detectors, thermocouples,voltage detectors, bypass conductors, and the like.

FIG. 8 is a schematic view of a fuel cell stack assembly 800 accordingto various embodiments of the present disclosure. Referring to FIG. 8,the fuel cell stack assembly 800 includes an upper block 603, a lowerblock 503, a fuel cell stack column 140, and side baffles 820. The sidebaffles 820 each include a first plate 802, a second plate 804, and athird plate 806, which may include ceramic materials. The plates 802,804, 806 may be formed of the same material and may have substantiallythe same size and shape. The plates 802, 804, 806 may be laminated toone another, such that the side baffles 820 have a laminate structure.However, according to some embodiments, the plates 802, 804, 806 mayinclude different materials and/or have different properties. Whilethree plates are shown in FIG. 16, the present disclosure is not limitedto any particular number of plates. The plates 802, 804, 806 may belaminated to one another in a horizontal direction that is perpendicularto a stacking direction of fuel cells of the fuel cell stack column 140.

For example, the third plate 806, which is closest to the fuel cellstack column 140, may have a higher dielectric strength than the firstand second plates 802, 804 disposed further from the fuel cell stackcolumn 140. The first plate 802 and or the second plate 804 may havehigher strength and/or rigidity than the third plate 806. As such, eachplate may be configured to impart specific features to the side baffle820. For example, one of the plates 802, 804, 806 may be formed of amaterial having a relatively higher thermal conductivity than otherplate(s). However, the present disclosure is not limited to the specificcompositions and/or characteristics, which may be altered according tospecific applications and requirements.

With regard to flow channels, ceramic components, such as side baffles,having a laminate structure can be configured such that certain layersform an internal manifold or channel(s). Such a structure may be used todeliver fuel to a fuel cell stack column, which can eliminate orsimplify existing fuel rails 214. Further, such an internal manifoldcould also be configured to direct air into and/or around the fuel cellstack column to improve temperature change characteristics of the fuelcell stack column. Accordingly, such structures may operate as airand/or fuel manifolds.

Manifolds or channels may be formed in a laminate ceramic component byforming holes in individual ceramic layers, and then connecting thelayers such that the holes are aligned to form a manifold or channel. Inthe alternative, one of the layers may be formed of ceramic strips, withareas between the strips forming a manifold or channel(s), inconjunction with other layers disposed on opposing sides of the strips.

FIG. 9 is a schematic view of a fuel cell stack assembly 900 accordingto various embodiments of the present disclosure. The fuel cell stackassembly 900 is similar to the assembly 800 of FIG. 8, so only thedifferences therebetween will be discussed in detail.

Referring to FIG. 9, the fuel cell stack assembly 900 includes sidebaffles 820. However, in contrast to FIG. 8, the second plate 804 atleast partially defines channels 808 that extend through the side baffle820. The channels 808 may extend in across the fuel cell stack column140 in a widthwise direction (i.e., the channels 808 may extendhorizontally (into or out of the page) in a direction perpendicular to alengthwise direction (vertical stacking direction) of the fuel cellstack column). The channels 808 may be configured to allow air to flowthrough the side baffles 820, and thereby cool the fuel cell stackcolumn 140. As such, the channels 808 may be referred to as “airchannels”.

The channels 808 may be equally spaced apart. However, according to someembodiments, the second plate 804 may include a higher density of thechannels 808 in areas that receive more heat. For example, the secondplate 804 may include more channels 808 in areas adjacent to the centerof the fuel cell stack column 140 than at areas adjacent to ends (e.g.,top and bottom) of the fuel cell stack column 140, which tend to becooler than the center of the stack column 140. According to someembodiments, the second plate 804 may be formed of ceramic strips thatat least partially define the channels 808.

According to some embodiments, a method of providing air to the stackassembly 900 is provided. In particular, air is blown horizontally intothe stack assembly (i.e., into the page) into an open face of the stackcolumn 140 and into channels 808. A portion of the air fed into thestack 14 is used as an oxidizer in an electrochemical power generationreaction, while a portion of the air is fed through the channels 808 tocool the stack column 140.

FIG. 10 is a schematic view of a fuel cell stack assembly 1000 accordingto various embodiments of the present disclosure. The fuel cell stackassembly 1000 is similar to the assembly 800 of FIG. 8, so only thedifferences therebetween will be discussed in detail. Referring to FIG.10, the fuel cell stack assembly 1000 includes a lower block 503 havinga layered structure. In particular, the lower block 503 includes aninlet manifold 812 and an outlet manifold 814. The inlet manifold 812may operate to supply fuel to the fuel cell stack column 140. The outletmanifold 814 may operate to receive reaction products from the fuel cellstack column 140. The laminate structure of the lower block 503facilitates the formation of manifolds, since it may be easier to formmanifold structures in the thinner individual layers of the laminatestructure, before assembling the layers together and forming a manifold.

The fuel cell stack assembly 1000 may also include a fuel channel 810that extends through the side baffle 820 and lower block 503. In someembodiments, the fuel channel 810 may also optionally extend through theupper block 603. An opening 822 of the fuel channel 810 may be connectedto a fuel source 818. The fuel source 818 may be a natural gas pipeline,a fuel storage vessel, such as hydrogen or hydrocarbon fuel tank, or anyother suitable source of fuel. The fuel channel 810 may be configured toreform a fuel e.g., to act as a fuel reformer or pre-reformer. Forexample, the fuel channel 810 may include a fuel reformation catalyst.The catalyst may be any suitable catalyst, such as a nickel/rhodium, forexample. Suitable catalysts are disclosed in U.S. Pat. Nos. 8,563,180and 8,057,944, which are incorporated herein, in their entireties, byreference. The catalyst may be coated on the inner surface of the fuelchannel 810 or may be disposed within the fuel channel 810.

The fuel channel 810 may be connected to the inlet manifold 812. Theinlet manifold 812 may be connected to a fuel inlet 824 of the fuel cellstack column 140. In particular, the fuel channel 810 may extend throughan inner layer of the lower block 503. However, in other embodiments,the fuel channel may extend to a lower surface of the lower block 503.The lower block 503 may also include a fuel outlet 826 of the fuel cellstack column 140.

FIG. 11 is a schematic sectional view of a fuel cell stack assembly1100, taken through a plane in which bypass electrodes and sensorsextend, according to various embodiments of the present disclosure. Thefuel cell stack assembly 1100 is similar to the assembly 800 of FIG. 8,so only the differences therebetween will be discussed in detail.

Referring to FIG. 11, side baffles 820 of the fuel cell stack assembly1100 include bypass electrodes 830 extending there through. The bypasselectrodes 830 may be connected to individual interconnects of the fuelcell stack column 140. For example, a bypass electrode 830 may beincluded (e.g., embedded in the side baffle 820) for each interconnectof the fuel cell stack column 140. Accordingly, the bypass electrodes830 can be electrically connected to one another, so as to electricallybypass selected fuel cells. As such, the bypass electrodes 830 allow thefuel cell stack column 140 to continue operating, in the case where oneor more fuel cells operate improperly or are damaged. The bypasselectrodes 830 can be connected by, for example, using an externalconnector 834. However, any suitable connection device or method may beused.

According to an alternative embodiment, rather than embedding the bypasselectrodes 830 into the side baffle 820, the side baffle may containopenings (e.g., vertically stacked, horizontally extending throughholes) which expose the side edges of the respective interconnects inthe fuel cell stack column 140. If a defective fuel cell is detected inthe stack, then the electrically connected bypass electrodes 830 areinserted into openings in the side baffles 820. The bypass electrodes830 are connected by a connector 834 and contact the respective sideedges of the interconnects located above and below the defective fuelcell in the stack.

The side baffles 820 may also include sensors 832. The sensors 832 mayextend through a side baffle 820 and contact the fuel cell stack column140. The sensors 832 may be imbedded in channels in a side baffle 820.The sensors 832 may be temperature sensors (thermocouples), pressuresensors, electrical sensors, e.g., lead wires for a current or voltagesensor, or the like.

FIG. 12A illustrates a perspective view of a portion of a fuel cellstack assembly 1200 (with the fuel cell stack column shown transparentlyfor clarity), according to various embodiments of the presentdisclosure. FIG. 12B illustrates a side view of an upper plate assembly750 of the fuel cell stack assembly 1200. FIG. 13 illustrates aperspective view of a rod plate 607 of the upper plate assembly 750. Thefuel cell stack assembly 1200 includes elements similar to the fuel cellstack assemblies described above, so only the differences therebetweenwill be described in detail.

Referring to FIGS. 12A, 12B, and 13, the fuel cell stack assembly 1200includes side baffles 202 connected to a compression assembly 700A thatis similar to the compression assembly 600A, and is disposed on theupper plate assembly 750. The compression assembly 700A includes a leafspring 611 and support rods 604, and is disposed on the upper plateassembly 750. The upper plate assembly 750 includes a rod plate 607, acolumn termination plate 27, and an interface seal 712. The terminationplate 27 is disposed on an end plate 716 of an uppermost a fuel cell ofa fuel cell stack column of the assembly 1200. The termination plate 27includes a column electrical contact (not shown). The end plate 716 isdisposed on an uppermost electrolyte plate 718 of the column.

The rod plate 607 includes grooves 714 in which the support rods 604 aredisposed. The rod plate 607 may also include a thermocouple slot 709. Athermocouple may be inserted into the slot 709 to measure columntemperature. The rod plate 607 may be formed of alumina or a similarceramic material. The rod plate 607 may have a thickness of at least 1mm. For example, the rod plate 607 may have a thickness ranging fromabout 1 mm to about 5 mm, or about 2 mm to about 4 mm, such as athickness of about 3 mm.

The support rods 604 are configured to support the spring 611. Thespring 611 is configured to apply pressure to the column, via thesupport rods 604, the rod plate 607, and the termination plate 27. Theinterface seal 712 is an annular seal disposed between the end plate 716and the termination plate 27, and is configured to prevent fuel in afuel riser opening in the end plate 716 from flowing between the endplate 716 and the termination plate 27. The interface seal 712 may beformed of a glassy material. The interface seal 712 may flow at atemperature of at least 650° C., such as a temperature ranging from 675°C. to 725° C., or 685° C. to 715° C. For example, the interface seal mayflow at a temperature of about 700° C.

Due to the nature of materials used in the stack assembly 1200, the loadduring first heat up of the stack increases to as high as 850 lbs, untilthe interface seal 712 disposed around a fuel riser opening in the endplate 716 flows and spreads out before setting. This load increases thebending stresses of rod plate 607, which may cause it to break. Thisresults in disturbing the load distribution in the stack, which may leadto a loss of contact between the end plate 716 and the termination plate27, leading to a loss or flickering of column voltage and/or a fuel leakat the top of the column.

FIG. 14A a finite element model (FEM) showing load distribution on thetermination plate 27 during maximum loading in the upper plate assembly750, i.e., when a maximum load is applied thereto during initial fuelcell system startup. FIG. 14B is a FEM showing vertical deflections ofthe termination plate 27 during maximum loading. FIG. 14C a FEM showingstress applied to the rod plate 607 during maximum loading.

Referring to FIGS. 14A and 14B, loading is shown to be concentratedaround edges of the termination plate 27, which results in thetermination plate 27 bending by over 200 μm. As such, the terminationplate 27 may lose contact with the end plate 716, which may result involtage loss.

Referring to FIG. 14C, stress is shown to be concentrated at an end of athermocouple slot 709 formed in the rod plate 607. In particular, amaximum stress applied to the rod plate 607 may be very close tobreaking strength of alumina which forms the rod plate 607. As such, thestress may result in fracturing of the rod plate 607.

FIG. 15 is a sectional view of an upper plate assembly 750A according tovarious embodiments of the present disclosure. The upper plate assembly750A is similar to the upper plate assembly 750, so only the differencestherebetween will be described in detail.

Referring to FIG. 15, the upper plate assembly 750A includes a rod plate607, a termination plate 27, and an interface seal 712. The terminationplate 27 is disposed on an end plate 716 of an uppermost fuel cell of afuel cell stack column. The end plate 716 is disposed on an electrolyteplate 718 of the uppermost fuel cell of the column. The upper plateassembly 750A also includes a shim 720 disposed between the rod plate607 and the termination plate 27.

The shim 720 may be formed of a ceramic or cermet material. The shim 720may have a thickness of at least about 10 mm. For example, the shim 720may have a thickness ranging from about 10 mm to about 40 mm, from about12 mm to about 20 mm, or from about 14 mm to about 16 mm. The shim 720may have a thickness of about 15 mm, according to some embodiments. Theshim 720 may be configured to support the rod plate 607, such that thebending stress (shown by arrows) applied to the rod plate 607 isreduced.

FIG. 16A is a FEM showing load distribution on the termination plate 27during maximum loading in the upper plate assembly 750A. FIG. 16B a FEMshowing vertical deflections of the termination plate 27 during maximumloading of the upper plate assembly 750A.

Referring to FIGS. 16A and 16B, it can be seen that the shim 720 spreadsout the load applied to the termination plate 27. In addition, as shownin FIGS. 14B and 16B, the shim 720 reduces the maximum bending of thetermination plate 27 by at least a factor of 10, such as by about 10 to18 times. Accordingly, it can be seen that the shim 720 reduces thepossibility of voltage flickering or loss and rod plate breakage.

FIG. 17A illustrates a modified rod plate 607A according to variousembodiments of the present disclosure. FIG. 17B a FEM showing loaddistribution applied to the rod plate 607A during maximum loading. FIG.17C a FEM showing bending deflection applied to the rod plate 607Aduring maximum loading. FIG. 17D is a chart comparing maximum stressapplied to the rod plates 607 and 607A, and corresponding bendingdeflections of the rod plates 607 and 607A and corresponding terminationplates 27, over time, during initial fuel cell system startup.

Referring to FIG. 17A the rod plate 607A is similar to the rod plate607. However, the rod plate 607A has an increased thickness. Forexample, the rod plate 607A may have a thickness of at least about 8 mm.For example, the rod plate 607A may have a thickness ranging from about8-13 mm, about 8-12 mm, from about 9-11 mm, or about 10 mm. As such, athermocouple slot 709 of the rod plate 607A may have a depth that isless than the thickness of the rod plate 607A. In other words, thethermocouple slot 709 may be in the form of a groove formed in a bottomsurface of the rod plate 607A rather than a through hole.

Referring to FIGS. 17B-D, the increased thickness of the rod plate 607A,as compared to the rod plate 607, results in a reduction of the maximumstress by a factor of about 3. In addition, the maximum stress does notoccur at the end of the thermocouple slot 709. Further, the maximumdeflection of the rod plate 607A is reduced by a factor of about three.Thus, the rod plate 607A is shown to provide better bending and stresscharacteristics, as compared to rod plate 607. In addition, it wasdetermined that, during initial operation of a fuel cell system, amaximum load and stress applied to system components does not exceed thepermitted load and stress, when the rod plate 607A is included.According, the rod plate 607A provides for a safe fuel cell systemoperation during initial turn on.

The termination plate 27 may be made of 446 stainless steel (SS 446) ora Cr/Fe alloy. SS 446 may include by weight, 73% Fe, 23.0%-27.0% Cr,1.5% Mn, 1.0% Si, 0.25% Ni, 0.20% Ni, 0.20% C, 0.04% P, and 0.03% S. TheCr/Fe alloy may include, by weight, about 94-96% Cr and about 4-6% Fe,such as 95 wt % Cr and 5 wt % Fe, which may be the same material as usedin end plates and interconnects in the column 140. However, the presentinventors determined that using the Cr/Fe alloy results in a reductionin stress applied to the thermocouple slot 709 and reduced bending oftermination plate 27 and rod plate 607, 607A.

As shown in FIG. 18, the stress applied using the Cr/Fe alloytermination plate 27 is below 300 MPa at a temperature of greater than550° C., while the stress applied to the SS446 termination plate 27 isgreater than 300 MPa between 550 and 690° C. Likewise, the Cr/Fe alloytermination plate 27 deflection is lower than that of the SS446termination plate 27 at the same temperature.

Any one or more features from any one or more embodiments may be used inany suitable combination with any one or more features from one or moreof the other embodiments. Although the foregoing refers to particularpreferred embodiments, it will be understood that the invention is notso limited. It will occur to those of ordinary skill in the art thatvarious modifications may be made to the disclosed embodiments and thatsuch modifications are intended to be within the scope of the invention.All of the publications, patent applications and patents cited hereinare incorporated herein by reference in their entirety.

What is claimed is:
 1. A fuel cell stack assembly comprising: a fuelcell stack; an upper block disposed on a first end of the fuel cellstack; a compression assembly comprising a spring disposed between theupper block and the fuel cell stack; a lower block having a laminatestructure and disposed on an opposing second end of the fuel cell stack;and first and second side baffles disposed on opposing sides of the fuelcell stack and extending from the upper block to the lower block, thefirst side baffle comprising first, second, and third baffle plates thatare laminated and bonded to one another in a horizontal stackingdirection that is perpendicular to a stacking direction of fuel cells inthe fuel cell stack, the second baffle plate being disposed between thefirst and third baffle plates, wherein the first, second, and thirdbaffle plates connect the upper and lower blocks, such that the springapplies a compressive load to the fuel cell stack, and wherein the lowerblock comprises: an inlet manifold connected to an inlet of the fuelcell stack; and an outlet manifold connected to an outlet of the fuelcell stack.
 2. The fuel cell stack assembly of claim 1, wherein: theinlet manifold is connected to a fuel inlet of the fuel cell stack and afuel source, to supply fuel from the fuel source to the fuel cell stack;the outlet manifold is connected to a fuel outlet of the fuel cell stackto receive fuel exhaust from the fuel cell stack; and the second sidebaffle comprises first, second, and third baffle plates that are bondedto one another in the horizontal stacking direction that isperpendicular to a stacking direction of fuel cells in the fuel cellstack, the second baffle plate being disposed between the first andthird baffle plates.
 3. The fuel cell stack assembly of claim 1, furthercomprising a fuel channel extending through the first side baffle andinto the lower block and the upper block, the fuel channel optionallyextending through the upper block, wherein the fuel channel is at leastpartially defined by the second baffle plate.
 4. The fuel cell stackassembly of claim 3, wherein the fuel channel comprises a fuelreformation catalyst and is connected to the inlet manifold.
 5. The fuelcell stack assembly of claim 1, wherein the first, second, and thirdbaffle plates of the first and second side baffles have differentstrengths, thermal conductivities, compositions, or any combinationthereof.
 6. The fuel cell stack assembly of claim 1, wherein the first,second, and third baffle plates are formed of a ceramic material.
 7. Thefuel cell stack assembly of claim 6, wherein a space between the firstand third baffle plates at least partially defines a fuel channelextending from the lower block to the upper block.
 8. The fuel cellstack assembly of claim 7, wherein the fuel channel is at leastpartially defined by the second baffle plate.